This invention relates to protein food products and more particularly to a method of forming structured protein food products from vegetable and/or animal protein substances.
A highly desirable goal in food processing has been to employ less desirable food materials which are highly nutritious, yet inexpensive, and processing these to result in highly appealing food products. Particular efforts have been directed toward the production of simulated meat products from vegetable and/or animal protein substances. Various degrees of success have been achieved by a variety of processes as is illustrated, for example, by U.S. Pat. No. 2,682,466 to Boyer involving spun filaments and U.S. Pat. Nos. 3,496,858 to Jenkins and U.S. Pat. No. 3,940,495 to Flier involving the extrusion of vegetable protein materials under conditions of elevated temperature and pressure into a zone of lower pressure to thereby expand the resultant material and produce an expanded, textured protein food product which is simulative of a real piece of meat when hydrated.
U.S. Pat. No. 3,920,853 discloses a process for the formation of structured protein food products wherein an aqueous slurry of protein material is frozen into ice crystal layers spaced apart by intermediate layers of slurried protein particles created by formation of the ice crystal layers. Freezing of the slurry causes all of the ice crystal layers to extend in a generally normalized direction to the area or part of the slurry which is contacted with a refrigerating medium. The ice layers cumulatively comprise an in situ matrix which spaces, molds and compresses the protein layers in striated fashion. Following freezing of the slurry the next process step is to remove the ice layers and fix the remaining protein layers into a striated arrangement which resembles actual muscle tissue. This is carried out by heating of the frozen slurry at a temperature sufficiently high to fix the protein layers and convert them to a substantially insoluble form while the slurry is in a frozen state. This results in removal of the ice crystal layers and provides protein layers arranged in striated fashion with lines of cleavage generally arranged in the same direction. This novel food product bears a close resemblance to meat as a result of this arrangement of striated protein layers.
U.S. Pat. No. 3,920,853 further discloses as a preferred embodiment, controlled freezing of the aqueous slurry to provide a controlled, directional heat exchange and achieve formation of the ice crystal layers in the slurry, which in turn molds the protein into layers. This directional heat exchange comprises placing the slurry in a predetermined configuration and contacting the slurry with a refrigerating surface or medium on at least one side while the remaining sides of the container are insulated to minimize heat exchange at these surfaces. This provides both ice crystal and protein layer formation in a direction generally normal to the uninsulated surface. This modification provides a satisfactory means of controlling the direction of ice crystal growth during the freezing process in order to achieve a particular degree of ice crystal formation and, hence, simulate a particular foodstuff.
The present invention represents an alternative to employing directional heat exchange in order to control formation of the ice crystal layers, and provides a means of controlling ice crystal formation in a consistent manner.